In recent years, various technologies have been developed to increase storage capacity in magnetic disk devices. In one of the technologies, magnetic disk devices use shingled magnetic recording (SMR) to write data. In shingled magnetic recording, magnetic disk devices write data to a disk such that the current track overlaps part of the previously written adjacent track (hereinafter, simply referred to as the adjacent track). When magnetic disk devices write data by shingled magnetic recording, the track density (tracks per inch: TPI) of disks can be improved in comparison with normal recording.
In magnetic disk devices, generally, disk eccentricity is generated due to, for example, an attachment error of a disk and a spindle motor. When disk eccentricity is generated, dynamic offset (DO) occurs. Specifically, when the disk makes one revolution, the read/write offset value changes within a single track. Thus, in magnetic disk devices, write dynamic offset control (WDOC) which adjusts the R/W offset value is performed in a write process to control the dynamic offset. When a magnetic disk device performs WDOC, the device measures the eccentricity, calculates a corrected value based on the measured eccentricity, and performs WDOC based on the calculated corrected value. The state of eccentricity of the disk may be changed by external impact, etc. When the state of eccentricity of the disk has been changed, the magnetic disk device measures the eccentricity again, calculates a corrected value based on the measured eccentricity, and performs WDOC based on the calculated corrected value.
In magnetic disk devices which employ shingled magnetic recording, when the corrected value differs between before and after the change of the state of eccentricity of the disk, the data written to the adjacent track might be erased.